Apparatus for monitoring the selection of chart recording and wavelength scanning speeds in a radiant energy analyzer

ABSTRACT

A spectrophotometer system having a first stepper motor driving a wavelength scanning mechanism and a second stepper motor driving a chart recorder, both motors being operative in response to pulses from a system clock. The clock frequency is successively divided by first and second cascaded, switch-selectable sets of frequency dividers. The output of the first divider is applied to the wavelength motor and determines wavelength scan speed. The output of the second divider is applied to the chart motor and determines chart scale expansion. A decoder monitors the frequency selections of the first and second sets of frequency dividers, and upon detection of a frequency selection outside the capability of the chart motor, the decoder provides an output which inhibits both motors. The decoder output additionally actuates a visual indicator to inform an operator of the invalid selection.

BACKGROUND OF THE INVENTION

This invention relates to radiant energy analyzers having chartrecording means, and more particularly to an analyzer, such as aspectrophotometer, having a first plurality of preselectable wavelengthscan speeds and a second plurality of preselectable chart expansionvalues.

In spectrophotometer systems a wavelength scanning device is utilized totransmit radiant energy of differing wavelengths through a sample tomeasure an optical characteristic of the sample (e.g. absorbance ortransmittance), this characteristic then being recorded in graphicalform on a chart recorder as a plot of optical characteristic (ordinate)vs. wavenumber or wavelength (abscissa). In such systems the wavelengthscanning device is driven by a motor at one of a plurality ofpredetermined speeds. The abscissa of the chart paper is likewisecontrolled by a drive motor which may drive either the chart paper withrespect to a marker or pen or vice versa, at one of a plurality ofpredetermined speeds to effect abscissa scale chart expansion. In thismanner an operator may selectively expand the abscissa scale to providegreater clarity in regions of interest where the spectrum may be crowdedor, alternatively, may reduce the abscissa scale for uncrowded regionsof the spectrum. In operation of the spectrophotometer, preciseregistration and synchronization of the wavelength scanning device andthe chart recorder is necessary so that the spectrum scanned is exactlyreproduced by the recorder to provide a clear and accurate spectrum ofthe sample being analyzed.

To provide the greatest flexibility in an instrument of this type theoperator should be given a wide selection of wavelength scanning speedsand a wide selection of abscissa scale chart expansions. Unfortunately,some of the selected combinations of scan speed and chart expansion maybe limited by the capability of the drive motors or may be otherwiseunusable by the system. A selected combination which exceeds the torquevs. speed capability of the chart motor, for example, could not beaccurately executed by the motor, and the resulting graphical plot forsuch a selection would be erroneous. Moreover, the necessarysynchronization and registration between the wavelength scanning deviceand the chart recorder would be destroyed by attempted execution of aninvalid selection, requiring the operator to interrupt system operationto re-register the wavelength scanning device and the recorder.

SUMMARY OF THE INVENTION

Accordingly, it is an object of this invention to provide a new andimproved radiant energy analyzer having a wide range of preselectablewavelength scanning speeds and chart scale expansion values.

It is another object of the invention to provide a radiant energyanalyzer having means for detecting invalid combinations of wavelengthscanning speed and chart scale expansion.

It is a further object of the invention to provide means for inhibitingsystem operation for invalid combinations of scanning speed and scaleexpansion.

It is a further object to provide means for simplifying operator controlof the system by indicating invalid selected combinations.

It is a still further object of the invention to provide means formaintaining precise registration between the wavelength scanning meansand the chart recording means.

The foregoing and other objects of the invention are accomplished byproviding a radiant energy analyzer having a first frequency responsivemotor driving a wavelength scanning device and a second frequencyresponsive motor driving one recorder chart paper and marker along theabscissa of the chart paper, with both said motors being operated from asystem clock. First and second sets of cascaded switch-selectablefrequency dividers successively divide the system clock frequency andsupply their respective outputs to the wavelength motor and the chartmotor. Wavelength scan speed and chart expansion, respectively, are setby switch selection of the first and second sets of frequency dividers.A decoder monitors the combinations of selections from the first andsecond sets of dividers and, for invalid combinations, inhibits both thefirst and second drive motors to maintain registration of the wavelengthscanning device and chart recorder, and additionally provides a visualindication to an operator of the invalid selection.

Other objects and advantages of the invention will be apparent from thefollowing description taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a spectrophotometer system according to theinvention;

FIG. 2 is a block diagram of a portion of the system of FIG. 1 showingthe wavelength scan speed dividers and chart scale expansion dividers;

FIG. 3 shows in tabular form combinations of scale expansion andwavelength scan speed identified as valid or invalid combinations; and

FIG. 4 is a logic diagram of a portion of the decoder used in the systemof FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawing and particularly to FIG. 1, aspectrophotometer system is illustrated which includes a source 10, abeam switching system 11, a monochromator 12 and a thermocouple 13. Thesource 10 may be any suitable device which produces radiation over thespectrum being analyzed. The beam switching system 11 includes halfmirrors 14, 15 which are rotated in synchronism, and reflecting mirrors16, 17, providing a sample beam path 18 and a reference beam path 19. Asample cell 22 is positioned in the sample beam path 18 for containingthe sample to be analyzed. Means for varying the intensity of the beamalong the reference beam path 19 is positioned therein. A typicalexample is comb 23 which is driven into and out of the reference beampath by a motor 24.

Monochromator 12 includes means for dispersing the beam passingtherethrough, shown here as prism 27, and slit 28 which permits only asmall fraction of the dispersed beam to impinge on thermocouple 13.Prism 27 is rotated by a scan motor 29 during the analysis to scan theentire spectrum of interest past the slit 28. Scan motor 29, as employedin this embodiment, is a frequency responsive motor such as a steppermotor which is rotated by means of discrete digital pulses, and has aspeed dependent upon the frequency of the pulses. Motor 29 is energizedfrom a wavelength motor driver 30 which is ordinarily set to operate themotor at a constant rate. A programmed change in scan speed over thespectrum is usually desired and is conventionally accomplished bycoupling the motor to the prism or other dispersing element by means ofa cam of appropriate contour.

Thermocouple 13 produces an electrical error signal proportional to thedifference in intensity of the beams traversing the sample path andreference path with the error signal cyclically varying at the beamswitching rate, which ordinarily is in the range of 5 to 20 cycles persecond. The error signal from thermocouple 13 is connected to anamplifier 36. The output of the amplifier 36 drives the comb motor 24,with the amplifier and motor functioning as the comb servo.

Demodulator 34 is operated in synchronism with the beam switching systemand converts the a.c. error signal to d.c. Various types of demodulatorsmay be used with a mechanical chopper preferred at the relatively lowfrequencies ordinarily encountered in such instruments. Period circuit35 is a low pass filter that limits the response rate of the comb servoand reduces the sensitivity of the instrument to sharp transients in theerror signal such as are ordinarily produced by noise. The time constantof the period circuit is selected as a compromise between the maximumresponse rate of the comb servo and the acceptable noise level andtypically is in the range of 1/4 to 16 seconds. The simplest form ofperiod circuit which is used in many instruments is a resistancecapacitance filter section comprising a series resistor and a shuntcapacitor.

Scan speed suppression is provided by utilizing an absolute valuecircuit 38 which produces a voltage whose magnitude is determined by theabsolute value of the error signal. This output is then transmitted to ahold-over circuit 40, the output of which controls the voltagecontrolled oscillator or system clock 42. The output of the system clock42 is a pulse train, the frequency of which is proportional to theabsolute value of the error signal. This output frequency is thendivided by switch-selectable wavelength dividers 44 to produce a pulsetrain at a suitable frequency for the selected scan speed forapplication to the wavelength motor driver 30 which drives wavelengthstepper motor 29. The pulse train output of dividers 44 is also appliedto switch-selectable chart dividers 46 which are connected in cascadewith dividers 44. The output pulse train from chart dividers 46, at asuitable frequency for the selected chart expansion, is applied to thechart motor driver 48 which, in turn, drives a chart stepper motor 50.The chart stepper motor 50 in turn drives a take-up reel 52 of chartpaper 54 having the sample spectrum graphically reproduced thereon by asuitable marker or pen 56, the pen position on the graph ordinate beingindicative of the optical characteristic of the sample 22 and the chartmovement along the graph abscissa being indicative of wavelength orwavenumber.

In accordance with the present invention, the wavelength dividers 44 andthe chart dividers 46 are monitored by means of a decoder 62 connectedto the dividers by respective cables 58 and 60. Decoder 62, as willhereinafter be discussed, monitors for invalid combinations ofselections of wavelength dividing frequency and chart dividingfrequency. Upon occurrence of an invalid combination, decoder 62provides an inhibit signal on cable 64 to both the chart motor driver 48and the wavelength motor driver 30 to inhibit operation of chart motor50 and wavelength motor 29, and thus inhibit the chart drive and thewavelength scan. Simultaneously with the inhibit signal, an indicatorlight 66 is illuminated on the instrument control panel for operatorviewing to inform the operator of the invalid combination.

Referring now to FIG. 2, the system clock 42 provides a train of pulsesoutput to wavelength dividers 44 comprising a first plurality or set ofswitch-selectable frequency dividers 68, 70, 72, 74, 76, 78 and 80, anyone of which can be placed in series with the output of the system clock42 by means of rotary switch 82. Additionally, the system clock 42output can be transferred directly over lead 84 to one terminal ofrotary switch 82, this terminal being designated "1,200" (1,200wave-numbers per minute). The remaining terminals are designated "600"for frequency divider 68, "300" for frequency divider 70, "150" forfrequency divider 72, etc. The frequency dividing values "A," "B," etc.,are predetermined frequency dividing values to provide the selected scanspeed designated by the appropriate contact of rotary switch 82. Theoutput transferred through rotary switch 82 then passes to the chartdividers 46 comprising a second set of frequency dividers (the divisionfactors being designated V, W, X, Y and Z) 86, 88, 90, 92 and 94, anyone of which is switch selectable by means of rotary switch 96 to placeone of the frequency dividers in series between rotary switch 82 andchart motor driver 48. Additionally, a bypass lead 98 is provided totransfer the output of wavelength dividers 44 directly to the chartmotor driver 48 with switch 96 at the "20X" position. The switchcontacts are designated .4X, 1X, 2X, 4X, 10X and 20X to indicate theabscissa scale chart expansion selections.

With the switches 82 and 96 in the positions illustrated, the output ofsystem clock 42 is transferred over lead 84 through switch 82 towavelength motor driver 30 to drive wavelength motor 29 and throughfrequency divider 92 to the chart motor driver 48 to drive the chartmotor 50. It is to be understood that although rotary switches 82 and 96are shown, mutually exclusive push-button switches can also be utilized,with one switch for each of the designated variables or parameters.

Referring now to the table of FIG. 3, the vertical axis representswavelength scan speed in wavenumbers per minute selected by switch 82,while the horizontal axis represents scale expansion values selected byswitch 96. Each possible combination of selected scan speed and scaleexpansion is designated "----" if it is a permissible or validcombination or is designated "NO" if it is an impermissible or invalidcombination, the invalid combinations being determined by designconstraints of the motors being utilized (e.g. torque vs. speedcharacteristics) or other factors rendering a given combinationunusable. In the instant embodiment scan speeds of 1,200, 600 or 300with a 20X chart scale expansion are invalid selections. Similarly, scanspeeds of 1,200 or 600 with a scale expansion of 10X are invalid as is ascan speed of 1,200 with a scale expansion of 4X.

Referring now to FIG. 4, a logic diagram of decoder 62 is shown andincludes AND gates 100, 102, 104, 106 and 108 as well as OR gates 110and 112. The logic diagram accomplishes the result shown in tabular formin FIG. 3 to provide an "inhibit" as well as an "indicator" signal atthe output of OR gate 112 in the event the conditions labeled "NO"exist.

The inputs to the logic diagram of FIG. 4 are only those inputs ofinterest and relate to the chart scale expansion multipliers 20X on lead114, 10X on lead 116 and 4X on lead 118 as well as the scan speedsettings of 1,200 on lead 120, 600 on lead 122 and 300 on lead 124. Inthe event the operator selects the 20X scale expansion with the 1,200scan speed, leads 114 and 120 go "high," these two inputs being providedto AND gate 104 to pass through OR gate 112 to provide an output thusinhibiting both wavelength drive motor 29 and chart drive motor 50 aswell as illuminating the indicator 66 to thereby inform the operator ofthe invalid selection. Similarly, if the operator selects 10X scaleexpansion with either the 1,200 or 600 scan speeds, AND gate 102 isenabled from lead 116 as well as from the OR gate 110 which is coupledto lead 120 and 122. Similarly, with a scale expansion selection of 4Xlead 118 is "high" and with a scan speed of 1,200 lead 120 is "high,"thereby enabling AND gate 100 which provides a signal through OR gate112 to provide the output. AND gate 106 is enabled with a scan speed of600 and a scale expansion of 20X while AND gate 108 is enabled with thesame scale expansion at a scan speed of 300. In any event, the logicdiagram of FIG. 4 effectively provides an output through OR gate 112 forthe invalid combinations of FIG. 3.

Applying the inhibit signal over line 64 to inhibit the drive motors 29and 50 for invalid frequency selection combinations prevents erroneousgraphical information from being plotted on chart 54. Significantly,both motors 29 and 50 are controlled to maintain accurate registrationbetween the wavelength scanning mechanism 27 and the chart 54. Whilesetting up the spectrophotometer or even during an actual plottingoperation, an operator can select or change any combination of scanspeed and chart expansion without affecting the scan and chartregistration. For example, the operator simply may temporarily increasethe scan speed to rapidly reach a narrow absorption band of interest andhaving reached the band reduce the scan speed and increase the chartspeed to provide greater abscissa expansion across the band width. If aninvalid combination of frequencies is selected in the process, bothchart motor 50 and wavelength motor 29 stop immediately and indicator 66tells the operator that the selected frequency combination is invalid.Thereafter the operator selects other frequency combinations until avalid combination is selected at which time the chart motor andwavelength motor are enabled to resume the plotting operation at thesame graphical point where the plotting had been previously inhibited.As a result, the continuity of the graphical recording is maintained, noerroneous information is plotted, and scan and chart registration ismaintained thereby eliminating the need to repeatedly re-register thewavelength scanning device and the chart recorder following each invalidselection. Moreover, operator control of the system is greatlysimplified by indicator 66 which immediately informs the operator of anyinvalid combination.

While in the preferred embodiment of the invention the inhibit line 64is connected to the motor drivers 30 and 48 to inhibit respective motors29 and 50, the inhibit line could be connected instead to other circuitcomponents to inhibit the same motors. Thus, for example, inhibit line64 is alternatively connected to the inhibit inputs sof the dividers 44and 46 (as illustrated by the dashed connections in FIG. 1) to inhibitthe output of each divider and thereby prevent operation of motors 29and 50. In another alternative, inhibit line 64 is connected to theinhibit input of the system clock 42 (as illustrated by a dashedconnection in FIG. 1) to inhibit the clock pulse output to the dividersand thereby prevent operation of motors 29 and 50. In addition, whileAND-OR logic has been illustrated in the preferred embodiment, it shouldbe understood that NAND-NOR or other logic arrangements could beemployed in the invention. Moreover, it will be apparent that whileparticular forms of the invention have been illustrated and described,various modifications can be made therein without departing from thespirit and scope of the invention. Accordingly it is not intended thatthe invention be limited except as by the appended claims.

I claim:
 1. In a radiant energy analyzer having a radiation source, amonochromator and a wavelength scanning mechanism therefor, and chartrecording means for moving a marker in relation to chart paper along anabscissa scale and ordinate scale for recording a waveform spectrum of asample, the combination comprising:a system clock having an output of apredetermined frequency; a first frequency responsive drive motor fordriving said wavelength scanning mechanism for continuously varying thewavelength output of said monochromator at various wavelength scanspeeds; a second frequency responsive drive motor in said chartrecording means for driving one of said marker and chart paper along theabscissa with respect to the other of said marker and said chart paper;a first set of frequency dividers switch selectable to place a frequencydivider thereof in series between said system clock output and saidfirst drive motor, said first set of frequency dividers havingpredetermined frequency dividing values for wavelength scan speedselection; a second set of frequency dividers switch selectable to placea frequency divider thereof in series between said first set offrequency dividers and said second drive motor, said second set offrequency dividers having predetermined frequency dividing values forabscissa scale expansion selection; and decoding means coupled to saidfirst and second sets of frequency dividers for providing an output inresponse to invalid combinations of selected dividers of said sets, saidoutput inhibiting said first and second drive motors.
 2. The combinationaccording to claim 1 wherein the output of said decoding means energizesindicating means for indicating to an operator that an invalidcombination has been selected.
 3. The combination according to claim 1wherein said first and second drive motors are stepper motors and saidsystem clock has a train of pulses output.
 4. The combination accordingto claim 1 including means for applying the output of the decoding meansto the system clock to inhibit the output of the clock.
 5. Thecombination according to claim 1 including inhibit inputs for said firstand second sets of dividers and means for applying the output of thedecoding means to said inhibit inputs to inhibit the output of said setsof dividers.
 6. The combination according to claim 1 including first andsecond motor drive circuits for driving said first and second drivemotors and means for applying the output of said decoding means to saidmotor drive circuits to inhibit said first and second drive motors. 7.In a radiant energy analyzer having a radiation source, a monochromatorand a wavelength scanning mechanism therefor, and chart recording meansfor moving a marker in relation to chart paper along an abscissa scaleand ordinate scale for recording a waveform spectrum of a sample, thecombination comprising:a system clock having an output of apredetermined frequency; a first frequency responsive drive motor fordriving said wavelength scanning mechanism for continuously varying thewavelength output of said monochromator at various wavelength scanspeeds; a second frequency responsive drive motor in said chartrecording means for driving one of said marker and chart paper along theabscissa with respect to the other of said marker and said chart paper;first frequency division means connected between said system clockoutput and said first drive motor and selectable to provide a pluralityof frequency division values for wavelength scan speed selection; secondfrequency division means connected between said first frequency divisionmeans and said second drive motor and selectable to provide a pluralityof frequency division values for abscissa scale expansion selection; anddecoding means for monitoring the frequency selections of said first andsaid second frequency division means and for providing an output inresponse to invalid combinations of frequency selections, said outputinhibiting said first and second drive motors.
 8. The combinationaccording to claim 7 wherein the output of said decoding means energizesindicating means for indicating to an operator that an invalidcombination has been selected.
 9. The combination according to claim 7including means for applying the output of the decoding means to thesystem clock to inhibit the output of the clock.
 10. The combinationaccording to claim 7 including means for inhibiting the frequencyselection by said first and second frequency division means, and meansfor applying the output of the decoding means to said inhibiting means.11. The combination according to claim 7 including first and secondmotor drive circuits for driving said first and second drive motors andmeans for applying the output of said decoding means to said motor drivecircuits to inhibit said first and second drive motors.